With that, this is the amp I was looking at. I know you can explain its features better than I can:
http://www.crutchfield.com/p_20610ZX705/Kicker-10ZX700-5.html?tp=14
The first thing to notice is the "CEA-2006 Compliant" statement. CEA-2006 isn't nearly as good as the IHF testing criteria, but is good enough for a non-audiophile car stereo. It's a WHOLE LOT better than numbers that have no relation to reality, that's for sure!
The 20-20,000Hz frequency range is the same as the IHF standard, which is good.
"RMS" stands for root mean square, which is the actual power level. Cheats often use other ways to measure power (e.g. "peak power") that are designed to give the largest numbers, but you'd never see anything close to those numbers while playing music. The power is measured at 1% distortion, which is a lot for modern audio equipment. However it's roughly as much as the finest loudspeakers produce, and in a running car it's probably barely noticeable. They measure at 4 Ohms, which seems to be cheating a little. The standard for decades has been 8 Ohms for consumer grade loudspeakers. Professional sound reinforcement systems sometimes run 2, 4 or more 8 ohm drivers in parallel, giving a nominal impedance of 4, 2 and even 1 Ohm, and pro sound reinforcement power amplifiers are designed to be most efficient at these lower impedances. But pro sound has no bearing on a car stereo!
The ideal power amplifier produces twice as much power when you cut the load impedance in half. So a 100W @ 8 Ohm amp would make 200W @ 4 Ohms, 400W @ 2 Ohms and so on. And in fact, many pro amps come pretty close to doing that. When an amp can't do that, it's a clue that the power supply has less capacity than those with greater power multiplication. For all practical purposes, this is a non-issue
as long as you operate within the linear range of the amplifier.
I don't know why the Kicker amp is rated at 4 and 2 Ohms. I'd think that since it's for use in cars, where space is limited and weight is an issue, they'd want to use higher impedance speakers, which require less (thinner) wire. For best sound quality, I advise bumping up the speaker wire thickness when using this amp. 12AWG (stranded) minimum at 4 Ohms.
Having the (presumably line level) crossover circuitry built into the unit is convenient. So is having independently adjustable filters, provided you have some need to use different cutoff points. Unfortunately the rolloff rate for the low-pass filter is twice that of the high-pass filter. This mismatch is a bad sign. OTOH, since it's not a Hi-Fi unit, it may be tolerable. Still it's a sign of poor design.
Unless you're using a Kicker brand subwoofer that requires the bass boost to be set to anything but 0, I'd keep it at 0. Chances are that your car subwoofer will be incapable of reproducing down to 40Hz. Don't think that you can get something for nothing either. If you crank up the gain at 40 Hz, the subwoofer will go nonlinear and produce high order harmonics in the midrange, causing that ricey mid-bass pop-pop-pop instead of a good solid bass note.
The "differential-balanced inputs eliminate noise from your vehicle's electrical system" claim is BS. Those are consumer grade RCA jacks, which are unbalanced. Total BS. Shouldn't be a problem though, as long as you use good quality line level interconnects. Still...why lie?
When it comes to powering the unit, I'd skip on the Kicker brand wires, and buy standard automotive large-stranded power cable. They recommend 4AWG power cable; I'd use 2AWG cable provided there's room to run it. In fact, I'd eschew the chassis ground, and run a pair of wires (one red, one black) straight to the battery terminals. You'll need special terminators to fit into the power-in plugs. Putting raw stranded wire in a screw-down part like that is a bad idea. You can get the wire and the terminators at Home Depot or a boat or RV shop. They're used for power inverters, which use similar plugs. It takes a special tool to crimp on the ends, so try to have that done where you buy them.
I see that the offer includes a free 1F capacitor. The thing about these booster caps is that the only way they can work is if you have insufficient power wiring between the battery and the amp. I would do the wiring right in the first place, and trade the cap to a friend for something else.
nline: for my ST before I knew what to go with, so don't feel bad.
